1. Field of the Invention
The present invention relates to a semiconductor device used for electronic equipment and particularly to a semiconductor device having a resistor and a manufacturing method therefor.
2. Description of the Related Art
Conventionally, a resistor made of a polycrystalline silicon film is manufactured by depositing the polycrystalline silicon film on a silicon substrate whose surface is oxidized or the like to form an insulating film, implanting in the polycrystalline silicon an impurity such as boron difluoride or phosphorous, and then etching the polycrystalline silicon into the phosphorous, and then etching the polycrystalline silicon into the resistor using a photoresist or the like as a mask. FIG. 3 is a plan view showing a polycrystalline silicon film resistor. An amount of the impurity implanted into a polycrystalline silicon film resistor 103 is determined by determining a length L 101 and a width W 102 thereof and then performing calculation using the length L 101 and the width W 102 of the polycrystalline silicon film resistor and a desired resistance value.
However, in recent years, high accuracy is required for the semiconductor device. The polycrystalline silicon film resistor manufactured by using a conventional manufacturing method involves a variation in resistance value, which prevents improvement in performance of the semiconductor device mounting the polycrystalline silicon film resistor therein, in particular, the semiconductor device for which absolute value accuracy of the resistor is required as in an A/D converter or the like.
The present invention has been made in view of the above-mentioned problem and an object of the present invention is to provide a semiconductor device capable of solving the above-mentioned problem, which includes a polycrystalline silicon film resistor having a reduced variation in resistance value with high accuracy, and to provide a manufacturing method therefor.
In order to achieve the above object, the present invention employs a means as described below.
The present invention employs a means for using an implantation amount of an impurity implanted into the polycrystalline silicon film resistor around the impurity implantation amount in which a sheet resistance value becomes minimum when manufacturing the polycrystalline silicon film resistor.
As a result of trial manufacturing of the present invention, as shown in FIG. 1, it is confirmed that the sheet resistance value of the polycrystalline silicon film resistor takes a minimum value with respect to a certain impurity implantation amount. The fact that there exists a minimum value of the sheet resistance value with respect to the impurity implantation amount means that even if the impurity implantation amount varies in the vicinity of the minimum value of the sheet resistance, the variation in sheet resistance value is kept small.
In the case where the impurity implantation amount is previously determined, in order to obtain a desired resistance value for the polycrystalline silicon film resistor, a relation may be utilized, which is expressed by the following equation:
R=xcfx81sxc3x97L/W
where
R indicates the resistance value of the polycrystalline silicon film resistor,
xcfx81s indicates the sheet resistance value of the polycrystalline silicon film resistor,
L indicates a length of the polycrystalline silicon film resistor, and
W indicates a width of the polycrystalline silicon film resistor.
When the impurity implantation amount is determined, the sheet resistance value of the polycrystalline silicon film resistor is determined. Thus, L/W, that is, the length and the width of the polycrystalline silicon film resistor may be determined so as to obtain the desired resistance value of the polycrystalline silicon film resistor.
With the above-mentioned structure, the polycrystalline silicon film resistor with a small variation can be obtained.